About UDIM show
In many videos on youtube you can see that uv-tiles (udim) are shown togather
But in my case all uv-tiles (udim) are shown separately
How to show all them simultaniously?
You are using one UDIM tile per texture set whereas the video shows more than one tile used per texture set (up to 4). So in both cases only one texture set is shown at any one time, it is just that in the video the texture set shown contains 4 UDIM tiles.